The present invention relates to a process for preparing 3,4-methylenedioxymandelic acid from 1,2-methylenedioxybenzene. 3,4-Methylenedioxymandelic acid is a useful compound as a starting material for synthesis of medicines, agrochemicals, and the like, and as a starting material for heliotropin used as general cosmetics and perfumes.
A process for preparing 3,4-methylenedioxymandelic acid by reacting 1,2-methylenedioxybenzene with glyoxylic acid in the presence of a strong acid such as sulfuric acid or phosphoric acid has already been known (for example, Japanese Provisional Patent Publication No. 95573/1979 which corresponds to U.S. Pat. No. 4,190,583, Perfumer and Flavourist, vol. 14, p. 13 (1989)). In the process described above, however, the product 3,4-methylenedioxymandelic acid is insoluble in this reaction system and thus precipitated as crystals and, as the reaction proceeds, the reaction solution is made highly viscous or solidified to make stirring very difficult. Another problem is that this reaction is an exothermic reaction, so that when the reaction solution is made highly viscous or solidified, the whole of the reaction solution is hardly cooled, and the temperature of the solution is partially increased to cause formation of byproducts, thus reducing the selectivity of 3,4-methylenedioxymandelic acid. In particular, this phenomenon occurs significantly when the reaction is in a large scale.
Japanese Provisional Patent Publication No. 95573/1979 supra describes that the reaction is carried out preferably in the absence of a solvent, and if necessary, addition of formic acid or acetic acid exerts an advantageous influence on the reaction. Thus, the type and effect of solvent are not described, and when an organic acid is used, the specific amount of the organic acid added is not described either. Accordingly, we made extensive study on this reaction and found that the problem described above can be solved by adding an organic solvent. Further, we unexpectedly found that when an organic acid is used, the formation rate and selectivity of 3,4-methylenedioxymandelic acid are significantly influenced by the amount of the organic acid added to 1,2-methylenedioxybenzene, and that there is the optimum amount of the organic acid added.
An object of this invention is to provide an industrially preferable process for preparing 3,4-methylenedioxymandelic acid, which can produce 3,4-methylenedioxymandelic acid in high selectivity by reacting 1,2-methylenedioxybenzene with glyoxylic acid and which can also be applied to the reaction in a large scale.
The present invention relates to a process for preparing 3,4-methylenedioxymandelic acid by reacting 1,2-methylenedioxybenzene with glyoxylic acid in the presence of a strong acid, characterized in that the reaction is carried out in the presence of at least one selected from the group consisting of an aprotic organic solvent and 100 to 1200 ml of an organic acid per kg of 1,2-methylenedioxybenzene.